1. Field of the Invention
The present invention relates to an ice making machine having a function or capability for preventing formation of imperfect ice such as so-called mush ice, slush ice or the like.
2. Description of the Prior Art
In a hitherto known ice making machine of the type in which water is recirculated over a surface of a freezing plate, as is illustrated in FIGS. 1 and 2 of the accompanying drawings, an evaporator 1a is provided on a rear surface of the freezing plate 1, and a water distributor 2 comprising a pipe of a circular section is disposed in the vicinity of and above the top end of the freezing plate 1, wherein water to be iced (hereinafter also referred to as ice making water) is sprayed over the freezing surface 1b of the freezing plate 1 from a number of orifices 2a formed in the lower peripheral portion of the water distributing pipe 2 in a linear array along the longitudinal direction thereof. With this arrangement, it is intended that the ice making water discharged from the individual orifices 2a of the water distributor 2 be distributed substantially uniformly over the whole freezing surface 1b, thus keeping temperature distribution gradients in the water flowing down over the freezing surface 1b to a possible minimum.
However, it has been observed that immediately before formation of ice on the freezing surface 1b of the freezing plate 1, so-called mush ice or slush ice which differs from a normal transparent ice slab in respect to various properties is likely to be produced on the freezing plate surface, as is discussed in detail in Japanese Laid-Open Patent Publication No. 96881/1980. When such mush ice or slush ice is formed, there arises a possibility that some of the orifices 2a of the water distributor 2 may be jammed by mush ice or slush ice, providing a great obstacle to forming a uniform ice slab over the freezing plate surface 1b. Consequently, ice pieces or ice cubes obtained from the cutting of the formed ice slab are degraded in geometrical configuration as well as ice quality.
Such being the circumstances, various approaches have been taken to prevent formation of mush ice or slush ice. For example, Japanese Laid-Open Patent Publication No. 53668/1980 discloses an arrangement in which a part of the ice making water before it is discharged over the freezing plate is supplied to the unfrozen ice making water leaving the freezing plate which may contain mush ice in order to eliminate such mush ice. However, this arrangement provides no fundamental solution to the problem mentioned above, because the formation of mush ice itself is not prevented. For this reason, the invention disclosed in the afore-mentioned Japanese Laid-Open Patent Publication No. 96881/1980 starts from the recognition that significant changes take place in various factors such as, for example, the temperature of the ice forming water, refrigerant and the like immediately before the mush ice is produced in the course of the freezing process and teaches that the amount of circulated water be decreased during a predetermined time interval by controlling the operation of a water circulating pump in response to output signals produced by sensor means such as thermostats, timers and the like which are designed to detect variations in such variable factors as mentioned above, to thereby form a nucleus of ice on the freezing plate surface so that an ice slab is formed over the whole freezing plate surface through an ice growing process starting from the ice nucleus. According to this procedure, formation of mush ice can be positively prevented, whereby the aimed object of this preceding invention is accomplished. Although the approach mentioned just above has an advantage over the first mentioned one in that formation of mush ice is thoroughly prevented, it still suffers drawbacks in that various elements are required for controlling the operation of the water circulation pump in addition to those for detecting the variations in the variable factors, involving high manufacturing costs for its embodiment.